1. Field of the Disclosure
The present application relates to an organic light emitting diode display device.
2. Discussion of the Related Art
Recently, a variety of flat panel display devices with reduced weight and volume corresponding to disadvantages of cathode ray tube (CRT) are being developed. The flat panel display devices include liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panels (PDPs), electroluminescent (EL) devices, and so on.
The electroluminescent devices are classified into an inorganic electroluminescent device and an organic light emitting diode (OLED) device on the basis of the formation material of a light emission layer. Such electroluminescent devices have features such as fast response time, high light emission efficiency, high brightness, and wide viewing angle because of using self-illuminating elements.
FIG. 1 is a mimetic diagram showing the configuration of an OLED.
As shown in FIG. 1, the OLED includes an organic electroluminescent compound layer configured to emit light in response to an electric field, and cathode and anode electrodes facing each other with the organic electroluminescent compound layer therebetween. The organic electroluminescent compound layer includes a hole injection layer HIL, a hole transport layer HTL, an light emission layer EML, an electron transport layer ETL, and an electron injection layer EIL. Such an OLED generates excitons by forcing electrons and electric-holes injected from the cathode and anode electrodes to be recombined with each other. Also, the OLED emits light using energies from the excitons which are transitioned from an excited state into the ground state.
The OLED is used in an OLED display device as a principal light emitting element. The organic electroluminescent compound layer is deteriorated by moisture and oxygen. As such, the OLED display device has a sealing structure shown in FIG. 2 to protect it from the environment. FIG. 2 is a cross-sectional view showing an OLED display device of the related art with a sealing structure.
The OLED display device of the related art includes an organic light emitting diode layer OLEDL on a substrate SUB. The organic light emitting diode layer OLEDL includes an organic electroluminescent compound layer EL (not shown). Also, the organic light emitting diode layer OLEDL is formed on a central area of the substrate SUB.
The OLED display device of the related art further includes pad portions PAD formed on edge areas of the substrate SUB. The pad portions PAD are used to receive and apply electrical signals from and to an external apparatus which is used to drive the OLED display device.
Also, the OLED display device of the related art includes a sealing glass substrate ENCAP that is combined with the substrate SUB using a sealant SEAL. The sealant SEAL is formed from an ultraviolet (UV) hardening resin material in boundary regions between the pad portions PAD and the organic light emitting diode layer OLEDL. The glass substrate ENCAP is used to prevent the intrusion of external moisture and oxygen and to protect the organic light emitting diode layer OLEDL.
Furthermore, because it is difficult to efficiently prevent the intrusion of external moisture using only the UV sealant SEAL, the OLED display device of the related art includes an absorbent GEL which is used to absorb intruded moisture and oxygen. The absorbent GEL is attached to a central region of the glass substrate over the organic light emitting diode layer OLEDL.
In this manner, the OLED display device of the related art protects the organic light emitting diode layer OLEDL using the absorbent and the sealant. However, a large-sized display device using the above-mentioned sealant GEL and sealing glass substrate ENCAP is limited in reliability.
Moreover, in order to ease interaction with a user, a flexible substrate may be used in the display device. To this end, it is necessary to develop a sealing member using a metal material rather than the glass substrate. Actually, a Korean patent publication number of 10-2011-0065777 discloses a thin flexible substrate, which is formed from a metal material, and a sealing member for efficiently protecting the organic light emitting diode layer. However, the sealing member that includes metal material can easily cause an electrical short between the pad portion and the OLEDL.
Meanwhile, the pad portion PAD can provide a path for transferring a variety of signals which are necessary to drive the organic light emitting diodes. The OLED display device includes a display area and a driving area. The display area is used to display images. The driving area has a driving portion which includes a variety of drivers used to drive the OLED display device. In detail, the driving portion includes a gate driver used to drive a plurality of gate lines, and a data driver used to drive a plurality of data lines. Also, the driving portion can include a timing controller used to control the gate driver and the data driver. Moreover, the driving portion can include a power supply portion used to supply a power voltage VDD to the gate and data drivers and the timing controller. The power supply portion derives the power voltage VDD from an input voltage Vin which is applied from an external power supply unit. In this manner, signal lines used to supply a variety of signals, which are necessary to drive the organic light emitting diodes, can be connected to a variety of drivers via the pad portions and a printed circuit board which is connected to the pad portions.
FIG. 3 is a planar view showing one area of the substrate in which a pad portion is formed. FIG. 4 is showing a burnt defect which is caused by a short circuit between a driving power pad VDD and a reference power pad VSS in the related art.
Referring to FIGS. 3 and 4, the pad portion is connected to a variety of electrodes on the substrate and used as a path for applying power voltages and a variety of signals, which control the display images, to the electrodes on the substrate. For example, the pad portion includes driving power pads VDD and reference voltage pads VSS that are formed on the substrate. Also, a sealant including a metal material can be formed on a region adjacent to the pad portion. In this case, a distance between the pad portion and the sealant is very small. Moreover, the distance between the pad portion and the sealant is further reduced by fabrication tolerances of each component. Due to this, an electrical short circuit can be generated between the pad portion and the sealant. If an electrical short circuit is generated between the pad portion and the sealant, the driving power pad VDD and the reference power pad VSS can be connected to each other. This condition can also increase the susceptibility of the OLED display device to electrostatic discharge (ESD). As such, an undesirable bright line, dark line, or driving fault can be generated.